Coined by G.I.'s in Vietnam. A reverse coping expression indicating that it means everything and I'm about to lose it. Usually used to dismiss witnessing or experiencing something so horrific that it can't be comprehended by the psyche. Alternately used as an expression of relief that one has avoided being killed even if they are injured or maimed.

Witnessing ones close friend be killed turning away and saying with a stone face ... it don't mean nothin`